In order to heat treat liquid products use is made of various types of heat exchangers in indirect heating. The most common types of heat exchangers are plate heat exchangers and tube heat exchangers. The method according to the present invention is applicable to both types, but is preferably intended for plate heat exchangers. Heat exchangers are also used to a considerable extent within the food industry, such as in dairies and in juice factories. Depending upon the temperature to which the product is heated, a pasteurised or a sterile product will be obtained.
A heat exchanger normally consists of different sections which all have two sides—one side for product and one side for a heating medium, such as water or other liquid at different temperature, or steam. Alternatively, the sections may be disposed regeneratively, so that a cold product is heated up by an already heated product.
It is naturally always desirable that both of the sides in each respective section are kept separate and discrete, but within the food industry this is extremely important. Otherwise, a ready-treated product may be reinfected by a heating medium or by untreated product.
Various methods of discovering leakage in a heat exchanger have been used with the passage of time, such as saline solutions and coloured water on the one side in a section and normal water on the other side, whereafter, by conductivity measurements of alternatively ocular observations, it has been possible to discover any possible leakage. These methods take up considerable time and another of their drawbacks is that it is difficult to discover minor leakage.
A further method is described in international Patent Specification WO 02/086438. This method implies that the heat exchanger is connected to an external unit with the aid of which different pressures are applied on the different sides in a section in a heat exchanger. The unit makes for the simultaneous testing of several sections. This method is effective as regards discovering minor leakage, but it is also time-consuming and involves external service costs, for example, for a dairy.